Third-grader Leila Fowler was killed Saturday afternoon April 27, 2013, in her home in the small town of Valley Springs, Calif. / Nicole Orlandi and Amy Hutt via KXTV

by Maneeza Iqbal, KXTV-TV, Sacramento

by Maneeza Iqbal, KXTV-TV, Sacramento

VALLEY SPRINGS, Calif. - Authorities on Saturday arrested the 12-year-old brother of an 8-year-old girl who died after being stabbed in her family's home last month.

The boy, who was not identified, will be charged with homicide, Calaveras County Sheriff Gary Kuntz said during a news conference Saturday. He did not release details on what lead detectives to the boy as a suspect in Fowler's murder.

"During the past 15 days, we have conducted an expansive investigation," Kuntz said. "These types of cases require a considerable amount of time. It was our commitment to make sure that we did as thorough a job as possible."

Leila Fowler was stabbed in her family's Valley Springs home on April 27. Her 12-year-old brother told investigators that a man broke into their home that afternoon while their parents were at a Little League game. The boy described the man as being tall with long gray hair.

The boy also told detectives he went to hide from the intruder in a different room, and found Fowler with severe injuries. Fowler was transported to the hospital where she later died.

A day before the 12-year-old was arrested, his mother described him as "protective" of his younger sibling.

On Friday, as speculation in the community built that perhaps the boy was involved, his biological mother told KOVR-TV, a Sacramento TV station, her son "could never hurt his sister."

"I've never seen him be mean to her," said Priscilla Rodriquez.

More than 2,000 hours were put into the investigation. Detectives studied several knives from the home to determine if one was used as a weapon in Fowler's death. The sheriff's department did not say from where investigators had recovered the knives but that the information would "come out eventually."

Dive crews also searched two small reservoirs near Fowler's home for additional evidence, while deputies canvassed more than 300 homes to see whether anyone may have remembered seeing anything the day of Fowler's murder. Police have said there was no sign of a burglary or robbery at the house.

Several days after the killing, hundreds of people gathered at Jenny Lind Elementary School where Leila was a popular 3rd grader. Her mother, Krystal Walters, tearfully thanked the crowd for the support.

"I just want to thank the entire community and all of our family and friends for all the overwhelming amount of support you've given our family," Walters said at the time. "It will never be forgotten. Thank you."

For a community still reeling from the killing, the news was another blow.

"It's bad enough to lose a child. I can't imagine losing a child by one of my own children," Patti Campbell, a longtime area resident and owner of Campbell's Country Kitchen, told The Associated Press.

Calaveras Unified School District Superintendent Mark Campbell said counselors will be available Monday at all schools.

The district "stands ready to provide whatever level of support and assistance is necessary to the Fowler family" and the community at large, he said.